The present invention relates to an ultra-wideband (UWB) receiver and also to a method and a system for transmitting data by implementing such a receiver.
Encoding and detection are the two key elements in all radio frequency communications systems.
In a narrow-band system, information is encoded by modulating a high frequency carrier of sinusoidal waveform, thereby facilitating radiation and propagation in empty space.
Since the modulation is very slow relative to the frequency of the carrier, the modulated signal retains its substantially sinusoidal waveform.
The multiple propagation paths that can exist between transmission and reception cause the received signal to be the result of superposing echoes of varying amplitudes and phase shifts. However the sinusoidal nature of the waveform of the transmitted signal ensures that this superposition remains substantially sinusoidal.
In this context, the signal can be detected on reception by correlation relative to a reference signal that can be generated locally within the receiver, since the waveform of the reference signal is known, being sinusoidal.
In an ultra-wideband communications system, communication can take place at a speed that is comparable to that of the frequency of the carrier used, or a non-sinusoidal impulse carrier can be used. Either way, the waveform of the modulated signal ceases to be sinusoidal in appearance.
The use of very short duration impulses as a carrier makes it possible not only to achieve very high speed transmission, but also to have an electronic embodiment that is potentially simplified since processing signals in such a system relies essentially on manipulating signals in the time domain, and such manipulations are easy to integrate monolithically in a very-large scale integration (VLSI) circuit.
In spite of these advantages, ultra-wideband systems raise difficulties in development because the short duration of a signal impulse requires it to be generated extremely rapidly and requires very fine time accuracy on detection.
Energy detection methods are not satisfactory, since an energy detector cannot distinguish between the wanted signal and noise, and presents sensitivity that is relatively low.
U.S. Pat. No. 6,763,057, the contents of which is incorporated herein by reference, describes an ultra-wideband data transmission system in which it is necessary to know the waveform of the received signal and to generate a reference signal. That system is therefore relatively complex.
In the past, the following publications: Multiuser interference and inter-France interference in UWB transmitted reference systems, 2004, Joint UWBST & IWUWBST, 2004, International Workshop on May 18-21, 2004, pp. 96-100 and Generalized transmitted reference UWB systems, Ultra-wideband Systems and Technologies, 2003, IEEE Conference on Nov. 16-19, 2003, pp. 147-151, the contents of which are incorporated herein by reference; have also made proposals to transmit ultra-wideband impulse doublets, the impulses being correlated and separated by a delay that is known accurately.
When the impulses of the doublet reach the receiver, both impulses have been subjected to the same waveform deformations and they remain correlated.
Reception includes a delay line for creating a delayed copy of the received signal, with the delay introduced by the delay line being the same as that between the impulses of the doublet. A correlator receives these two signals and generated a detected signal.
That method eliminates the difficulty of generating the reference signal, however implementing the delay line is complex. In addition, the delay is not easily programmable and the delay line presents a length that makes it practically impossible to integrate in a miniature circuit.